U.S. Pat. No. 5,886,822 discloses an ophthalmic lens presenting a projection insert. Such a projection insert is constituted by an optical imager for shaping light beams delivered by an electronic and optical system for generating light beams from an electronic signal, of the miniature screen, laser diode, or light-emitting diode (LED) type. The optical semiconductor directs light beams towards the eye of the wearer in order to enable information content to be viewed.
An example of a prior art display is shown diagrammatically in greater detail in FIG. 1.
By way of example, the optical imager is of the same type as described in above-mentioned U.S. Pat. No. 5,886,822.
An electronic signal carrying information is brought to a miniature screen 1 by a cable 7. On the basis of this signal, the miniature screen 1, illuminated by a background projector, generates a pixel image corresponding to the information. By way of example, it is possible to use a “Kopin Cyberdisplay 320 color” screen generating images comprising 320×240 pixels and having dimensions of 4.8 millimeters (mm)×3.6 mm. The screen 1 is held by a mechanical interface 3 in position relative to the optical imager 5. A protective shell 4 protects all or part of the assembly. The screen 1 is associated with optical components 8, in this case a mirror and a lens.
The optical imager 5 comprises a propagation prism 5a, a counter prism 5b, a quarterwave plate 5c, and a spherical Mangin mirror 5d. The spherical Mangin mirror is a plano-spherical lens whose spherical face has been made reflecting by aluminum plating treatment or the equivalent.
The imager 5 also includes polarization separator treatment 6 which may be implemented in the form of a deposit of thin layers either on the propagation prism 5a or on the counter prism 5b, or by means of a film stuck between the two above-mentioned elements.
The imager 5 is embedded in a molded lens 9 and the housing is placed facing forwards against the back of the lens, with reflection treatment 5e then being included in the lens. On the same principle, the housing could be disposed to one side of the lens 9, and then the reflecting element 5e would be absent.
The word “lens” is used in particular for an optionally correcting lens suitable for mounting in a frame for eyeglasses. This ophthalmic lens presents conventional functions such as correcting eyesight, and coatings against reflection, dirtying, scratching, etc.
FIG. 1 shows an ideal position for the eye O centered on the outlet optical axis A of the imager, with the image also being centered on said axis A. Such a perfect position can be achieved by positioning the imager 5 accurately in or on the lens 9 for a given user. Nevertheless, such a lens fitted with an imager and generally mounted in a frame for eyeglasses or an equivalent support must be suitable for being used effectively by a plurality of wearers presenting different morphology.
In particular, pupil spacing, i.e. the distance between the two pupils of the wearer, varies from person to person. As a result, for a given pair of information eyeglasses, a problem arises as shown in FIG. 2.
This figure shows only the lens 9 with the counter-prism 5b, the quarterwave plate 5c, and the spherical Mangin mirror 5d, represented by a cube 5A referred to as a “combiner”. The combiner 5A acts like a window, and for an eye O that lies off the optical axis A, as shown in FIG. 2, the combiner blocks some of the light rays because of its defined dimensions. This results in a vignetting phenomenon which is an optical effect that darkens certain portions of the image I, in general its periphery, and which makes it difficult to observe. As shown in FIG. 2, only the portion P of the image can be seen correctly by the eye O.